Piston



Oct. 9, 1934.

R. K. MULFQRD PISTON original Filed Ap'ia 231930 2 sheets sheet l M W zz RNEY Oct. 9, 1,934. R. K. MULFQRD PISTON Original Filed April- 23, 1930 2 Sheets-Sheet 2 ATTORN Y` Patented Oct. 9, 19734A NETE@ STATES PATENT @TYCE PISTON Application April 23, 1930, Serial No. 446,433 Renewed September 2, 1931 10 Claims.

This invention relates to pistons and especially aluminum or aluminum alloy pistons for internal combustion engines, having new and improved form and functions.

The principal novel features and improvements include; A skirt structure Which is physically integral, and is also preferably integral with other main parts such as the head and pin bosses, but is functionally practically independent of the head and bosses, and consists or" two main parts partially divided at opposite sides of the piston Aand supported from the head or bosses by struts of such form that when heated they expand laterally and are so connected to the main parts of the skirt that the latter` are brought together, or the entire skirt is in eiect contracted to an extent approximately proportionally to the increase in temperature. v

By this means the skirt as Well as the head portion of the piston may have a proper running nt or clearance in the cylinder when cold, and this proper it or clearance will be maintained up to any maximum operating temperature.

The head is provided with internal reeniorcing ribs or anges which also connect it to the pin bosses and are so designed as to provide not only the desiredv mechanical strength and stiffness, but to properly and ediciently transfer heat from the top wall of the head to the side Wall and rings and so to the cylinder surface which is cooled by the water jacket, with further transfer of remaining heat through the bosses without undue heating thereof and from the bosses to the skirt supports and skirt; oras otherwise described, the skirt members of thin section running-on comparatively cool portions of the cylinder wall are cooled to a relatively low temperature and draw heat from the pin bosses through the supporting struts so that the bosses are kept at a desirably low temperature and the oil lubricating the` pin is kept at correspondingly low temperature and high eiciency.y

The advantages of aluminum or aluminum ailoy pistons, such as lightness, reduced inertia effects and vibration, beneficial effect upon other features of engine design, high coe'icient of heat conduction for cooling, etc., are well understood in the art, but in design and use of such pistons various difficulties or disadvantages have developed, some of which will be brieiiy mentioned. Aluminum or suitable aluminum alloys have, as stated, a high coeflicient of heat conduction, and also a correspondingly high expansion coeicient, especially as compared with iron; so that in a piston with a continuous or unsplit skirt, thel running clearance when cold must be relatively great in order that there may be an approximately correct running i'lt when hot and this occasions piston slap while cold, and is likely to cause an excessively tight rit` when hot oreven binding or 60. scoring when overheated. it has been attempted to overcome these dimculties by splitting the skirt longitudinally in one or more places, thus providing for yield, or variation in skirt diameter; but

in the absence of additional means or devices, as presently referred to, if the skirt clearance or running fit is made p-roperly tight when cold, the pressure on the cylinder wall increases greatly when heated, thus correspondingly increasing engine friction and reducing eiliciency. In at- 7o tempts to properly adjust such divided or split pistons to compensate for temperature variations, connecting members of iron or steel have been incorporated in various Ways, which are intended to function by drawing together portions of the skirt. as the temperature rises and so to maintain the proper iit or clearance; but the radical difference in physical characteristics and especially in the expansion coemcient between suchferrous connectors and the aluminum or aluminum alloy of the piston makes it diicult or practically impossible to tightly and permanently connect these portions together; so that in many cases the connecting or adjusting elements become loose in service and other diiculties are encountered, as understood by skilled persons. Also, the design of aluminum pistons with a split skirt is in some cases such that expansion or contraction of the skirt causes disalignment of the pin bosses, cutting of the pin bearings, etc. The design of such pistons has also generally been such that proper transfer of heat from the head to the skirt or away from the bosses is not accomplished.

These and other difficulties are overcome in the present piston, in which the skirt, While an integral structure and also preferably integral with the head and bosses, is functionally separate from the head and is amply flexible or contractile in radial directions, and the integral but functionally movable parts of which are connected to heatextensible supporting struts extending from the bosses in such manner that as the piston heats the struts expand and the skirt parts are contracted or drawn together in proportion to the 105 amount of heating; so that the skirt may have a proper ruiming fit Without slap when cold and will be automatically readjusted to proper running t for any degree of running heat, without necessity for any separate expansion controlling 11o members, such as the ferrous inserts above referred to.

The reenforcing ribs or flanges in the head are also designed for proper transfer of heat from the head through the bosses and struts to the skirt and effective absorption of heat by the cylinder wall as sufficiently referred to above and hereafter.

The characteristics and advantages of the invention are further suiiciently explained in connection with the following detail description of the accompanying drawings, which show one representative embodiment. After considering this example, skilled persons will understand that many variations may be made without departing from the principles disclosed, and I contemplate the employment of any structures that are properly within the scope of the appended claims.

In the drawings: f

Fig. l is a side elevation of a piston embodying the invention in one form.

Fig. 2 is a section at 2 2, Fig. 1, enlarged.

Fig. 3 is a section at 3 3, Fig. 2.

Fig. 4 is a section at 4 4, Fig. 2.

Fig. 5 is a section at 5 5, Fig. 2.

Fig. 6 is a section at 6 6, Fig. 2.

Fig. 7 is a section at 7 7, Fig. 2.

The piston is preferably, as shown, a single, integral casting of aluminum or suitable aluminum alloy, although various features of the head, boss and skirt structures are new and valuable without regard to the integral construction.

lead 10 includes the top wall 11 and side wall 12 having any desired number of ring grooves 13. The pin bosses 14 are integrally connected at their outer ends at 14:L to the head side wall, and are additionally connected to the head, top and side walls by ribs or flanges especially designed to provide proper mechanical strength and at the same time to secure proper heat conduction or transfer away from the hot center of the top wall to the side wall and bosses and struts to the skirt. These ribs or anges include boss supporting flanges or arms 15 in planes transverse to the pin axis, extending convergently down from the top and side walls and connected to inward ends of the bosses 14, and center and side flanges 16 and 17 respectively, in planes at right angles to the arms 15, that is, in planes intersecting the pin axis. The inner edges of these iianges 16 and 17 are curved in generally ovate form, as at 18, to provide a desired cross sectional area of the anges at different points from the top wall center down to the bosses, and the arrangement of the flanges is such as to provide practically equal heat conducting distribution of the anges in relation to the head, top and side Walls, with the result that these flanges rst conduct heat from the hot head center laterally to the side wall of the head for transfer to the relatively cool cylinder wall through the shortest available heat conducting paths, thus disposing of the greater amount of heat, a relatively small amount being transferred through flanges and arms 15 to the bosses and conducted or radiated therefrom, as later referred to.

The skirt 20, as previously stated, is preferably an integral structure and integral with the head and bosses, but functionally consists of'two main parts 21 and 22 divided at each side of the piston by a sinuous slot or slit, producing intertting tongues or strips 23, 24, 25, 26 and 27 of the respective skirt portions.

Skirt supporting struts 30 integral with the bosses depend therefrom and are in cross section of curved or approximately semi-ovate form, including curved side walls 3l and 32 and usually also including a central stiffening or reenforcing rib 33 which may taper downward, as best shown in Fig. 2 to merge with the sectional outline of the strut proper at its bottom edge. Opposite sides or side edges of the struts are connected alternately to ends of the intertting skirt strips. Thus, as shown in the cross sections, Figs. 4 to 7, taking one side of the piston, as shown in Fig. 1, the upper strip 23 is connected at its free end to the edge Wall l31 of the corresponding strut 30 (Fig. 4) while the free end of the corresponding strip 23a of the other skirt portion terminates with slight clearance adjacent this point of connection.

Similarly, each alternate strip, that is all the strips 23, 25 and 27 of the skirt part 21 are connected to the sameside of the corresponding strut, and the edge of the other strut wall 32 is free from the adjacent strips as at 34, Fig. 6, while the strips 24 and 26 of the other skirt section are connected to the edge of the other strut wall 32 and free from the adjacent strips as at 34, Fig. 6, while the strips 24 and 26 of the other skirt section are connected to the edge of the other side wall 32 of the strut (as sufficiently shown in Fig. 7).

In operation, as the piston heats, the struts, on

account of their curved or bowed form, extend' laterally or tend to straighten in their transverse planes, thus causing all the strip ends which are connected to either wall of the strut to move toward the free ends of the adjacent strips of the otherl skirt section; or in eiect, moving the two skirt sections convergently, and contracting the skirt in proportion to the degree of heating, thus preserving the proper running fit at all operating temperatures and enabling the skirt to have a proper iit without slap when cold and maintaining this t as the piston heats, and also avoiding at all times an extensive pressure of the skirt on the cylinder wall. rhe automatic adjusting v of the skirt diameter in accordance with temperature may be varied or controlled by varying the cross sectional area of the struts, or their form or degree of curvature.

The skirt is connected to the rest of the piston structure only at the points of connection to the strut walls which are of small area. The skirt is therefore kept comparatively cool and tends to disseminate heat from the bosses and struts to the relatively cool cylinder wall by radiation, as A well as by conduction and convection, so that the temperature of the lubricant on the pin is kept low. As shown in Figs. 1 and 2, holes 40 are provided in the skirts at opposite sides in line with the bore of the bosses, this being merely to permit proper machining of the boss bores.

The pin bosses are supported rmly, directly from the head, and the skirt portions are so flexibly connected to the bosses through the struts that expansion and contraction, due to heating, has no tendency to disalign the bosses, and cramping of the pin bearing is avoided.

The described construction permits full advantage to be taken of the light weight of the aluminum piston without increased weight caused by ferrous inserts for thermal expansion control, or other disadvantages connected with such inserts and at the same time, secures automatic adjustment Vof skirt diameter in accordance with temperature variation and desired effective heat transfer from the head.

I claim:

1. A piston comprising a head, pin bosses, skirt supporting struts extending downward from the head and bosses, and skirt sections including interspaced strip portions having ends connected to the struts and supporting the skirt sections thereon for relative expansion and contraction.

2. A piston comprising a head, pin bosses, heatexpansible struts of curved cross section depending from the bosses, and functionally independent skirt portions having interspaced strip portions connected to edges of the expansible struts in relatively opposite arrangement whereby strut expansion produces relative contraction of the skirt parts and automatically adjusts the skirt running clearance in accordance with temperature variations.

3. A piston of light weight metal comprising a head, pin bosses, and intercrossed anges connecting the bosses to the top and side walls of the head, the flanges having generally ovate inner edge contours providing substantially uniform heat transfer from the top to the side wall of the head.

4. A piston of light weight metal and of integral construction, comprising a head, bosses, heat expansible struts depending from the bosses, and functionally independent skirt sections connected to the bosses, the skirt portions including interspaced relatively narrow strip portions having at each side similarly located ends connected to one edge of the adjacent strut and having at the other side free ends adjacent and unconnected to the other edge of the other strut.

5. A piston of light weight metal and of integral construction, cornprising a head, bosses, heat expansible struts depending from the bosses, and functionally independent skirt sections connected to the bosses, and the skirt portions including interspaced relatively narrow strip portions having at each side similarly located ends connected to one edge of the adjacent strut and having at the other side free ends adjacent and unconnected to the other edge of the other strut.

6. A piston of light weight material comprising a head, pin bosses, skirt supporting struts extending downwardly from the head, a skirt divided into two separate semi-cylndrical sections having overlapping edges, two adjacent overlapping edges being attached, respectively, to opposite Vertical edges of a supporting strut, each supporting strut having the part between its vertical edges bowed inwardly away from the circumference of the skirt, whereby horizontal strut expansion draws the two semi-cylindrical skirt sections relatively inwardly towards each other.

7. A piston of light weight metal and of integral construction, comprising a head, bosses, functionally independent skirt sections, struts connecting the bosses to the skirt sections, and support and heat conducting anges connecting the bosses to the head, the struts being of approximately semi-ovate form in cross-section and each having an apex and extremities and being of progressively decreasing thickness from the apex to the extremities.

8. A piston of light weight metal and of integral construction, comprising a head, bosses, functionally independent skirt sections, supporting and heat conducting flanges connecting the bosses to the head, the struts being of approximately semi-ovate form in cross-section and each having an apex and extremities and being of progressively decreasing thickness from the apex to the extremities, and a downwardly and inwardly tapering central reinforcing rib at the apex of each strut.

9. A piston comprising a head, pin bosses, heat expansible struts of curved cross-section depending from the struts, at least two functionally independent skirt portions assembled to form a cylindrical skirt, the extremities of said skirt portions being connected to opposite edges of opposite struts whereby expansion of the struts causes movement of the sections to reduce the relative diameter of said cylindrical skirt.

10. A piston of light weight material comprising a head, pin bosses, a plurality of flanges parallel to the axis of the pin bosses and connecting the bosses to the top and side wall of the head, a plurality of flanges at right angles to the axis of the pin bosses and connecting the bosses to the top and side wall of the head, said flanges having their inner edges curved in generally ovate form to conduct heat uniformly from the top wall of the head to the side wall and to the bosses.

RALPH K. MULFORD. 

